1. Field of the Invention
This invention relates to cutting blades, such as those used to perforate or sever a paper web and, more particularly, to an assembly for holding a blade on a carrier therefor in such a manner that assembly, disassembly and adjustment of the blade are facilitated.
2. Background Art
There are many environments in which cutting blades are used. In one exemplary system, cutting blades are used to perforate or sever a continuous paper web. In these types of systems, it is known to provide a rotary cylinder with at least one slot through a peripheral surface thereof that defines the blade mounting location. The slot typically has a circumferential dimension that is substantially greater than the thickness of the blade so that the slot will accommodate both the blade and a holding assembly for the blade.
A myriad of different blade holding assemblies have been devised and remain in use today. Most of these assemblies are designed to fit loosely within the slot together with the blade and are reconfigurable to be captively held, together with the blade, in the slot.
With the blade in an operative position on the cylinder, the blade projects radially beyond the peripheral cylinder surface. As the cylinder rotates, the cutting edge on the blade is brought repetitively into close proximity to an underlying anvil to penetrate a web moving between the blade and the anvil. The blade may be configured to make perforating cuts in the web or to cut fully through the web. The cylinder diameter and location of the blade(s) on the periphery of the cylinder are selected to produce a desired spacing between successive cuts as the cylinder rotates.
Specifications for many cutting operations demand that the size and depth of the cuts produced by the blade be precise. This may necessitate that the blade be sharp and consistently oriented on the cylinder at all times.
To maintain a sharp blade, regular sharpening or replacement may be required. In most cases, this will involve removal of the active blade for sharpening or replacement. To replace the active blade, the holding assembly is reconfigured to allow the blade to be released. The same reconfiguration of the holding assembly is required to adjust the blade, which must initially be loosened and then re-secured after the appropriate reorientation has been carried out.
The design of the blade holding assemblies is key to efficient overall system operation. Blade replacement and adjustment both require that the cylinder be stopped, in turn requiring that the entire system operating in conjunction with the cutting cylinder be shut down.
While minimizing down time is a key consideration in the design of a blade holding assembly, it is also important that a holding assembly be capable of positively holding a blade precisely in its intended orientation. Any compromise on the blade position may lead to faulty cutting and/or premature blade failure, both of which compromise overall system performance.
An overriding objective in the design of blade holding systems is that they be user friendly. Systems that are difficult to operate, or in which blade adjusting procedures are time consuming, will inevitably encourage users to avoid this task. As a result, improperly aligned blades and dull blades may be left in place longer than is practical.
One exemplary prior art system is shown in U.S. Pat. No. 4,131,047 (Schriber et al). In Schriber et al, the user is required to rotate a relatively large number of screws to reconfigure the blade holding apparatus to release the blade and to re-secure the blade. In the one embodiment, five such screws are shown which apparently must each be loosened and tightened to adjust and replace the blades. Aside from the inconvenience of having to turn that many screws, the system appears to be prone to blade misalignment. Since there is no practical way to place and maintain the blade and blade holding system in a desired orientation and simultaneously tighten the screws, the screws must be tightened one by one. If the first screw is tightened with the blade system misaligned, there may be no way to straighten the blade without loosening the first tightened screw. The user may tighten a large number of the screws and only then determine that there is a misalignment of the blade which may require that all of the tightened screws be loosened and re-tightened. Rather than loosen the screws to carry out the necessary alignment, the user may be tempted to proceed with a misaligned blade.
Other exemplary systems are shown in U.S. Pat. Nos. 3,527,123; 3,705,526; 3,935,774; 4,131,047; 4,475,425; 4,594,928; 5,224,408; 5,275,076; 5,282,409; and 5,357,836.